Bring a large pot of lightly salted water to a boil. Add pasta and cook until tender but still firm, about 8 minutes. Drain.
Meanwhile, melt 1 tablespoon (20g) of butter in a wok or large frypan over medium-high heat. Add chicken pieces; cook and stir until browned. Season with Cajun seasoning, and remove the chicken from the wok and set aside.
Melt the remaining butter in the wok over medium-high heat. Add the garlic and onion; cook and stir until fragrant and beginning to brown. Add the green, red and yellow capsicum strips and season with chilli flakes, curry powder, salt and pepper. Cook and stir until the capsicum is hot. Return the chicken to the wok and pour in the pasta sauce. Heat through and serve over pasta.